Atomic Raman scattering: Third-order diffraction in a double geometry

Abstract

In a retroreflective scheme with an atom initially at rest, atomic Raman diffraction adopts some of the properties of Bragg diffraction due to additional couplings to off-resonant momenta. As a consequence, double Raman diffraction has to be performed in a Bragg-type regime, where the pulse duration is sufficiently long to suppress diffraction into spurious orders. Taking advantage of this regime, double Raman allows for resonant higher-order diffraction. We study theoretically the case of third-order diffraction and compare it to first order as well as a sequence of first-order Raman pulses giving rise to the same momentum transfer as the third-order pulse. Moreover, we demonstrate that interferometry is possible, and we investigate amplitude and contrast of a third-order double Raman Mach-Zehnder interferometer. In fact, third-order diffraction constitutes a competitive tool for the diffraction of ultracold atoms and interferometry based on large momentum transfer since it allows one to reduce the complexity of the experiment as well as the total duration of the diffraction process compared to a sequence, at the cost of higher pulse intensities.

Atom interferometry with quantized light pulses

“…Even though atomic Raman diffraction is a two-photon process [37][38][39] stimulated by two counterpropagating light fields, it can be modeled by an effective two-level system 36,37 coupled to a single running wave 40 . In contrast to the conventional semiclassical treatment, we consider in this article a quantized light field.…”

“…Moreover, we neglect effects from off-resonant (detuned) diffraction or velocity selectivity 38,39 . This treatment is justified when light shifts are compensated [47][48][49] , and for experiments that work with sufficiently short pulses or sufficiently cold atom clouds with narrow momentum distributions, either generated by velocity selection 50 or by utilizing Bose-Einstein condensates 51 .…”

Bragg-diffraction-induced imperfections of the signal in retroreflective atom interferometers

“…The approach can in principle be applied to double Raman diffraction too, where the Raman-Nath regime does not show such a rich structure [15], but higher-order diffraction is possible as well [59]. Furthermore, since the cancellation of diffraction phases was caused by the symmetry of the Mach-Zehnder interferometer, it might be worthwhile to check whether other geometries like Ramsey-Bordé-type setups display similar symmetries [37].…”

Bose-Einstein condensates in microgravity and fundamental tests of gravity

“…The inverse scaling with k eff T 2 in Equation (6) suggests two strategies to decrease ∆g: (i) Large-momentum transfer techniques (LMT) resulting in large effective wave vectors k eff and (ii) increasing the interrogation time T . With the former strategy considerable progress has been achieved over recent years with higher-order Bragg and Raman diffraction [74,75], sequential Bragg diffraction [76,77], Bloch oscillations [78][79][80] and combinations [81] which has resulted in an enormous increase of the space-time area enclosed by the branches of the interferometer [76,[82][83][84]. However, spurious diffraction phases [85] and parasitic interferometers [86] arise which are hard to control.…”